Polyepoxide resins are widely known and have wide applications for use in automobile parts, springs, pipes and in the preparation of composite articles, as for example. by wet filament winding, compression molding, reaction injection molding and other techniques. They find such use because of their hardness, resistance to solvents and water, adhesion to metals and other surfaces, and other properties.
Conventionally, epoxy thermoset polymers are formed by reacting a glycidyl polyether of a polyhydric phenol with an amine, the amine acting as a curing agent for the epoxy resin. A wide variety of primary and secondary amine curing agents have been reported for use in curing epoxy resins in order to adjust the pot life of the epoxy resins for molding or winding, to impart long-term color stability and to impart resistance to sunlight and so forth. Primary amines are used to form crosslinked epoxy resins while secondary amines are used to formulate linear polyepoxide resins or used to react with polyfunctional epoxides to form crosslinked resins. Representative patents which show a variety of both aromatic and cycloaliphatic primary and secondary amines for use in preparing polyepoxide resins are as follows:
U.S. Pat. No. 3,321,438 discloses aliphatic and cycloaliphatic amines, including piperazines, as curing agents for fluidized bed polyepoxide coating compositions. Examples of alkyl-substituted diamines include: diethylene triamine, dimethyldaminodicyclohexylamine. propylenediamine and triethylene tetramine; cycloaliphatic diamines such as di(3-methyl-4-aminocyclohexyl)methane and di(4-aminocyclohexyl)methane and the N-substituted derivatives, e.g. N-cyclohexyl-1,3-propane diamine. Representative piperazines include aminobutylpiperazine and N-aminoisopropylpiperazine.
U.S. Pat. No. 2,817,644 discloses various curing agents for polyepoxides which comprise hydrogenated aromatic primary and/or secondary polyamines. Aromatic amines in their hydrogenated form include phenylenediamine, p,p'-methylenedianiline, 2,4-diaminotoluene, and N,N'-diphenylethylenediamine.
U.S. Pat. No. 3,629,181 discloses various cycloaliphatic and cycloaliphatic-aliphatic di-primary amines as a curing agent for polyepoxides. Representative di-primary amines include 1,4-diamino-3.6-diethylcyclohexane. 2,2-di(4-aminocyclohexyl)-propane, which is commonly referred to as hydrogenated bisaniline A, and 1-amino-3-aminomethyl-3,5,5-trimethyl-1-cyclohexane, which is commonly referred to as isophoronediamine.
U.S. Pat. No. 4,417,010 discloses a process for producing epoxy resins using liquid imidazole type curing agents. Many imidazole type curing agents were alleged as being difficult to use because they were solids or because they were too reactive resulting in premature gelation. Solvents were often used with the solid imidazole curing agents to enhance the effectiveness and this usually required higher temperatures and longer reaction times to drive off the solvent. By combining N,N'-dihydroxyethyl-5,5'-dimethyl hydantoin or trimethylpentanediol with a solid. eutectic forming imidazole, a liquid curing agent was obtained. Examples of imidazoles suited for use included 2-ethyl-4-methylimidazole and 2-phenylimidazole.
U.S. Pat. No. 4,447,586 discloses a process for producing polyepoxide resins using, in combination, a meta fluoborate (fluoroborate) and a hindered aromatic amine curing agent. Examples of liquid or low melting hindered aromatic amines include: diethyltoluenediamine, methylenebis(2,6-diisopropylaniline), methylenebis(2,6-diethylaniline) and methylenebis(2-methyl-6-ethylaniline).
U.S. Pat. No. 4,686,250 discloses a process for the preparation of moisture resistant wet winding epoxy resin systems using a polynuclear aromatic diamine or substituted derivative thereof as a curing agent. Examples of aromatic diamines include: 1,3-bis(4-aminophenoxybenzene), (TPE-R), and alpha,alpha'-bis(4-aminophenyl)-para-diisopropylbenzene.